Physics

Problem

A pebble A is dropped from rest from the top of a

80\,\text{m}

tower. One second later, pebble B is projected vertically downward from the same point with a speed

u

so that both pebbles strike the ground at the same instant. Ignore air resistance and take

g = 10\,\text{m/s}^2

. The value of

u

is approximately a)

8.3\,\text{m/s}

11.7\,\text{m/s}

21.7\,\text{m/s}

10.0\,\text{m/s}